1. Field of the Invention
This invention relates to a magneto-optical disk apparatus for recording and reproducing information such as images on a magneto-optical disk.
2. Related Background Art
As a magneto-optical disk apparatus for recording and reproducing image information or the like on a magneto-optical disk, there is known one shown in FIGS. 1 and 2 of the accompanying drawings as disclosed, for example, in U.S. Ser. No. 427,959 filed Oct. 25, 1989 (now U.S. Pat. No. 4,998,238 issued Mar. 5, 1991), which is a continuation application of U.S. Ser. No. 172,678 filed Mar. 24, 1988 (now abandoned) by the same assignee as the assignee of the present application.
FIG. 1 shows a magneto-optical disk which is a recording medium, and FIG. 2 shows the construction of a magneto-optical disk apparatus.
The magneto-optical disk 1, as shown in FIG. 1, is divided into an outer recording area 1a and an inner recording area 1b, and as shown in FIG. 2, is rotated at a constant speed by a spindle motor 2. At lower locations opposed to the outer and inner recording areas 1a and 1b of the magneto-optical disk 1, magneto-optical heads 13a and 13b endowed with the erasing and reproducing functions and magneto-optical heads 14a and 14b endowed with the recording and reproducing functions are disposed divisionally at circumferentially different positions (for example, positions different by 180.degree.).
The erasing and reproducing magneto-optical heads 13a and 13b are carried on a head slider 7 which is moved radially along a slider rail 11 by a slider driving magnet 9 so that the outer recording area 1a can be traced by the magneto-optical head 13a and the inner recording area 1b can be traced by the magneto-optical head 13b.
This also holds true of the recording and reproducing magneto-optical heads 14a and 14b, that is, the magneto-optical heads 14a and 14b are carried on a head slider 8 which is movable radially along a guide rail 12 by a slider driving magnet 10.
Permanent magnets 15 and 16 are disposed at upper locations opposed to the magneto-optical heads 13a, 13b and 14a, 14b, respectively, with the magneto-optical disk 1 interposed therebetween. The permanent magnet 15 applies, for example, a downward extraneous magnetic field as an erasing magnetic field to the magneto-optical disk 1, while the permanent magnet 16 applies an upward extraneous magnetic field as a recording magnetic field to the magneto-optical disk 1.
First, during the recording operation, the recording areas of the magneto-optical disk 1 are erased by the magneto-optical heads 13a and 13b, prior to recording. This erasing operation is accomplished by applying a light spot of a strong laser beam from the magneto-optical heads 13a and 13b to the corresponding recording areas of the magneto-optical disk 1 to heat the recording areas to a critical temperature or higher, and making the direction of magnetization uniform downwardly (in the direction of arrow A) by the extraneous magnetic field by the permanent magnet 15 in the cooling process of the magneto-optical disk 1.
When that portion of the magneto-optical disk 1 which has thus been erased makes about one half of one full rotation and arrives at the position of the recording and reproducing magneto-optical heads 14a and 14b, the disk 1 is heated to a critical temperature or higher by the application of a light spot of a laser beam modulated by a recording signal, for example, the application of a light spot corresponding to the recording bit "1", and in the cooling process thereof, the direction of magnetization is reversed to the upward (the direction of arrow B) direction of magnetization by the extraneous magnetic field of the permanent magnet 16, whereby the recording operation is accomplished.
During reproduction, either the magneto-optical heads 13a, 13b or the magneto-optical heads 14a, 14b are used as reproducing heads, and a light spot of a weak laser beam is applied, for example, from the magneto-optical heads 13a, 13b to the magneto-optical disk 1, and the direction of polarization of the reflected light therefrom which depends on the direction of magnetization is read to thereby reproduce the recording signal.
However, in such a conventional magneto-optical disk apparatus, the transfer rate of the recording signal and the recording time have been fixed in dependence of the number of recording heads and therefore, for example, in an apparatus directed to the recording and reproduction of the standard quality of monochromatic image, there has been the problem that the reversible reproduction of the high quality of monochromatic image or the standard quality of colored image which requires a higher transfer rate cannot be accomplished.
That is, when viewed with the 3:1:0 component system directed to the standard quality of colored image in which a Y signal, a B-Y signal and an R-Y signal are sampled and recorded at sampling frequencies three times, 0.5 times and 0.5 times as high as the color sub-carrier wave frequency Fsc as the standard, the standard quality of monochromatic image can be regarded as the so-called 2:0:0 component system in which the Y signal, the B-Y signal and the R-Y signal are sampled as twice, 0 times and 0 times respectively the color sub-carrier wave frequency Fsc, and the high quality of monochromatic image can likewise by regarded as the so-called 4:0:0 component system in which the Y signal, the B-Y signal and R-Y signal are sampled as four times, 0 times and 0 times, respectively, the color sub-carrier wave frequency Fsc, and in an apparatus directed to the standard quality of monochromatic image, recording and reproduction of the high quality of monochromatic image or the standard quality of colored image which requires a transfer rate twice as high as the conventional one cannot be accomplished.